R E S E A R C H @ H K U S T
29
cubic meters collected through a deep,
23.6 kilometer system of tunnels.
Inside the treatment plant, high
concentration chlorine (10%) is injected
into a “flowing river of treated sewage”
in the form of multiple dense jets. While
chlorine is an effective disinfectant for
reducing pathogen levels, it is toxic to
the marine environment and aquatic
life. Actual operation shows that the
chlorine concentrations fluctuate in a
complex manner, and a good part of
the chlorine is consumed by organics
in the sewage rather than killing the
pathogens. This is both costly and
environmentally unfriendly.
To study the challenging problem,
Prof Lee and his team designed and
constructed a full-scale hydraulic
model at the Stonecutters plant. “At the
end of the day, the best theories have
to face the test of reality. You can’t just
talk about principles,” he said. “That’s
really what engineering is all about –
integration of theory and practice.”
Findings have recently been
reported in the
Journal of Environmental
Engineering
in which Prof Lee
outlines a theory for the mixing
and chemical reaction of a chlorine
jet with CEPT effluent, explains
the puzzling chlorine consumption, and
proposes various chlorine optimization
strategies.
Prof Lee has served as expert
consultant on numerous hydro-
environmental projects and contributed
to the design of several major
urban environmental management
and flood control infrastructure in
Hong Kong, including the Tai Hang
Tung Storage Scheme, Yuen Long
Bypass Floodway, and the Hong Kong
West Drainage Tunnel.
Top:
The field-scale model at Stonecutters Island
Sewage Treatment Works for studying chlorine
dosage optimization in Hong Kong’s wastewater.
Bottom:
Theoretical model of dense chlorine jets
in sewage flow for dosage optimization.
U
a
,P
a
,S
0
Z
X
D
U
0
,C
0
,P
0
B(x)
U(x)
s
ø
V(x)
W(x)
ds C(x), S(x)
z(x)
Coflow jet
region
Advected line
thermal
CEPT sewage
inflow from
sedimentation tank
Head
tank
Discharge of sodium
hypochlorite solution
Dosing unit
Test flume
Outlet tank
A Good Day to
Go to the Beach?
The WATERMAN coastal water quality
forecasting and management system,
masterminded by Prof Lee, has provided
a new way of dynamically coupling near
and far field models using a Distributed
Entrainment Sink Approach (DESA).
This has enabled a robust and seamless
simulation of the transport and fate of
pollutants from the point of discharge to
sensitive receivers (for example, bathing
beaches) located kilometers away.
In practice, the WATERMAN system
has become the first to predict coastal
beach water quality in real time, with
field validation, providing daily water
quality forecasts for 16 Hong Kong
beaches through the internet and a
smartphone app. Based on statistical
and 3D deterministic hydrodynamic and
water quality models, it has achieved over
80% accuracy in forecasting compliance/
exceedances with Hong Kong’s Water
Quality Objectives.
In addition, WATERMAN enhanced
communication, decision-making
and emergency response through the
development of a 3D environmental
impact assessment system using hydro-
environmental modeling and visualization
technology; and took forward scientific
management of fisheries through providing
a prediction of the carrying capacity of
Hong Kong’s 26 fish culture zones.
The project, funded by the Hong Kong
Jockey Club Charities Trust, was awarded
to Prof Lee in 2009 while at the University
of Hong Kong. He continued to pursue the
research after moving to HKUST
in 2010, with a trial system
becoming accessible
to the public in 2011.
Related publications
have appeared in the
Journal of Fluid Mechanics,
Water Research
and
Journal of
Environmental Engineering
, among others.
The WATERMAN
system provides a daily
forecast of beach water quality,
disseminated to the public through
the internet and a smartphone app.
Big Wave Bay
Deep Water Bay
